This invention relates to a pressurisable container having a safety device for releasing excessive container pressure. In particular, the invention relates to the general type of pressurisable container having a pressure release outlet, a rupturable closure element closing the outlet, a cutting device arranged to rupture the closure element when a predetermined maximum pressure in the container is exceeded, a rigid retaining device which holds the cutting member in a position out of engagement with the closure element when the container pressure is less than the predetermined maximum pressure, and a predetermined weakening provided on the retaining device which breaks when the predetermined maximum pressure is exceeded so as to allow the cutting device to move under the action of the pressure in the container to rupture the closure element.
Many types of safety devices against excessive pressure in a container are known. In addition to valves there are devices which have thin areas which break open in the event of excessive pressure, devices which are fitted with plane or concave-convex rupture discs, devices which have shearing plugs, or devices which contain closing elements which can be destroyed by explosive force.
According to respective requirements, safety devices are also frequently used which are each provided with a concave-convex, membrane-like closing element, which is placed against a cutting device in the event of excessive pressure and is cut open by this. However, these devices only operate satisfactorily when the rise in pressure acting on the closing element is relatively fast. If the pressure increases gradually, the minimum cutting action required to cut through the closing element is not always achieved. Existing safety devices with which the closing elements are pushed, changing their shape, against a cutting device by the prevailing pressure in the container, must be manufactured with extreme precision and require, as well as a sufficiently fast rise in pressure, the closing element to have a particular geometry and particular material properties if they are to operate satisfactorily (see German Pat. Nos. DE-A 2 828 341,2 706 723, 2 540 597).
A safety device against excessive pressure in a container (of the general type referred to above) is known. In the case of one embodiment of this known safety device, which is constructed in the manner of a valve, the internal pressure of the container acts on one side of the closing element. A valve disc is adjacent to the opposite side of the closing element, and this disc is under spring pressure and has cutting points for cutting the closing element. According to a second embodiment. the spring can be omitted in the case of the known safety device, and the valve disc can have the form of a plunger, whose free shaft end engages with a cross bar wich is in turn gripped at both ends and has a desired pressure point on its rear side. Under the condition that the plunger, according to the second embodiment, is provided with cutting points according to the first embodiment, the known safety device operates in such a way that the closing element moves against the cutting points in the event of excessive pressure in the container, is cut open by them and breaks the cross bar at the point provided therefor, so that the plunger exposes the whole valve cross-section for a release of pressure. Here too, however, a relatively fast rise in pressure in the container is required if the cutting points are to be effective. If the pressure rises gradually, the closing element moves against the cutting points without being cut. The arrangement is such that only a round, outwardly deflectable closing element can be used (see U.S. Pat. No. 2,079,164).
In another safety device against excessive pressure in a container, a closing element is provided in which, if excessive pressure occurs, this closing element can be cut open by a tubular cutting device which is retained in the initial position by a lever and is held under spring pressure. The lever can pivot out of its initial position to release the cutting device by means of an expensive manostat device. The arrangement is sluggish however (see French Pat. No. 2 044 512).
Another safety device against excessive pressure contains a closing element that can be cut open with a tilting blade. In the event of excessive pressure, the tilting blade can be swivelled into the tilting position with an actuating rod which engages with a membrane arranged in its rear under the pressure prevailing in the container. This safety device is also very expensive, and the cutting device is retained in the initial position only by virtue of a force-fit (see U.S. Pat. No. 3,279,647).
Another safety device against excessive pressure in a container operates in such a way that an annular, two-position catch spring holds a hollow-cylindrical blade in one catch position against the pressure of a medium acting on a membrane designed as a closing element. If the pressure exceeds the strength of the catch spring, the membrane bulges outwards and moves the catch spring into its other catch position by means of intermediary members. The catch spring then jolts the blade against the membrane, and the latter is destroyed and the desired release of pressure results (see U.S. Pat. No. 3,482,732).
Safety devices similar to the art described above are known from the following: French Pat. Nos. 2 252 519; 1 595 660; 2 355 226; German Pat. No. 568 051; published German patent applications 2 727 935; 1 790 137; and U.S. Pat. Nos. 1,970,718; 3,145,573. The arrangement described in these patents and published patent applications are less similar to the general type of container with which the invention is concerned, than the above described safety devices.